1. Technical Field
The present invention relates to a rectifier bridge assembly for an air-cooled generator and a method of producing such a rectifier bridge.
2. Description of the Related Art
It is known that excessive heat accumulation can cause the rectifier of an automotive generator to malfunction. Moreover, increased underhood ambients, coupled with increased generator output have led to growing demands on the heat sink capability of automobile generators. In addition to thermal difficulties, vibration that occurs during the usage of automobile generators can cause fatigue failures in terminal assemblies of bridge rectifiers.
Furthermore, usage also often loosens the B+ cable connection to the battery output terminal of a rectifier bridge. Typically, such a connection comprises a ring terminal for the B+ cable secured through a threaded fastener attached to the positive heat sink. During field usage, the connection may loosen due to relaxation of the clamp force.
Conventional bridge rectifiers for automobile generators are known, as seen by reference to U.S. Pat. No. 5,640,062 issued to Yockey. Yockey discloses an alternator assembly with an internal bridge rectifier. The bridge rectifier disclosed by Yockey includes a plurality of positive diodes, a plurality of negative diodes, and a plurality of conductive traces to electrically connect pairs of positive and negative diodes to stator lead wires, or stator phase windings. Yockey further discloses solder pads within the conductive traces to receive anodes of positive diodes, cathodes of negative diodes and stator lead wires. In addition, Yockey discloses a battery terminal that is electrically connected to and extends out from the bridge rectifier.
The arrangement of solder pads in the bridge rectifier disclosed by Yockey radially and angularly increases the size of the bridge rectifier. Moreover, the rectifier bridge disclosed by Yockey may not adequately retain the B+ cable connection to the output terminal.
In addition, present production heat sinks are typically stamped aluminum plates with a variety of holes and opening configurations. These openings permit airflow through the rectifier and at the same time provide surface area for convective heat transfer. However, because of the limitations of a flat, stamped heat sink, the amount of surface area that can be realized is limited. Alternatively, if sufficient surface area is provided, then the heat sink itself can be too large to fit within the room available, either in a radial or axial direction.
There is therefore a need to provide an improved rectifier bridge that overcomes one or more of the above identified shortcomings.
The present invention provides an improved compact rectifier bridge for an alternating current generator. A compact rectifier bridge in accordance with the present invention comprises a first electrically conductive heat sink with a first diode electrically coupled to the first heat sink. The first diode has an electrical lead extending from the diode. The invention further comprises a second electrically conductive heat sink axially spaced from the first heat sink, and a second diode electrically coupled to the second heat sink. The first and second diodes have an electrical lead extending from each diode. The invention further comprises a diode terminal assembly sandwiched between the first and second heat sinks for electrically insulating the first and second heat sinks from each other. The diode terminal assembly has a lead terminal for electrically connecting leads from the first and second diodes. The lead terminal is radially spaced from the first and second diodes.
The present invention may also comprise an output terminal structure, associated with the first heat sink, for supporting an alternator output terminal. The output terminal structure may comprise a compressible tower disposed about an output terminal stud and a cavity in the surface of the first heat sink for receiving the output terminal stud. The walls of the cavity may rotationally secure the output terminal stud.
The present invention also provides a method of manufacturing a compact rectifier bridge. The method comprises the steps of providing a first electrically conductive heat sink; electrically coupling a first diode to the first heat sink; providing a second electrically conductive heat sink axially spaced from the first heat sink; electrically coupling a second diode to the second heat sink; sandwiching a diode terminal assembly having a lead terminal between the first and second heat sinks, the diode terminal having a lead terminal; and electrically coupling the leads of the first and second diodes to the lead terminal, the lead terminal, which is radially positioned relative to the first and second diodes.
One object of the present invention is to overcome the foregoing problems and/or to satisfy at least one of the aforementioned needs. One advantage of the present invention is that it provides a rectifier bridge with a high ambient temperature capability in a compact assembly. The invention achieves this through the layout geometry of the rectifier bridge which affords a relatively small package size, both with respect to height and angular span, and low thermal resistance. In particular, opposing sets of press-fit positive and negative diodes may be stacked in line and facing each other. For rectifier bridges that require, for example, 12 diodes the diode arrangement of the present invention frees up angular space, as each diode set does not require as much angular arc in the layout. Additionally, the layout geometry of the present invention shortens the overall axial length of the rectifier bridge assembly due to a radial connection of the diodes instead of an axial connection. With the diode pair facing each other, the diode leads are bent and brought out in a substantially radial manner where they are welded to the terminal assembly. In contrast, in conventional rectifier assemblies, diodes project axially from the back surface of a heat sink to connect to the terminal assembly. Such a configuration requires additional axial length in the assembly due to the distance required for the typical terminal connection.
In addition, the terminal assembly of the present invention consists of an overmolded copper strap disposed within a plastic structure. This structure is sandwiched between the positive and negative heat sinks. The terminal assembly is clamped in place by axially projecting spacers from the positive and negative heat sinks. Through this configuration, the terminal assembly of the present invention is held rigidly and securely to resist vibration induced fatigue failures. Moreover, the configuration of the terminal assembly in the present invention provides a convenient location for the diode leads from a pair of positive and negative diodes that straddle the insert molded terminal assembly. As a welded joint, the leads themselves serve as a natural concentration point for welding, as opposed to welding a lead to a flat plate. Furthermore, since both leads must be in intimate electrical contact with the strap for welding to occur, the invention provides for an additional degree of error proofing to the connection of the leads to the terminal assembly.
The present invention further provides an improved B+ connection. The invention provides a cast tower around the B+ output terminal. In the invention disclosed, the B+ output terminal is a bolt that is retained by a cavity that is molded in the underside of the positive heat sink of the rectifier. Advantageously, the cast tower acts like a mechanical spring when the B+ cable is connected. When the B+ connection is tightened, the tower compresses. As a result, although during field usage actions such as creep, thermal expansions and contractions, vibration, and the like may occur, the tower acts like a spring and provides adequate clamp force so that good electrical contact is maintained.